Especially for complex Integrated Circuit (IC) chips and IC chips with arrays with a large number of devices, device leakages can overwhelm chip power be. A general application of leakage reduction techniques impairs performance and has been equally unpalatable. Accordingly, some designs use multiple supplies or a variable supply to selectively reduce supply voltage, e.g., supply one voltage during memory access and a second, lower voltage when memory cells are not being accessed.
Thus, some higher performance chips use on-chip voltage converters, e.g., switched-capacitor circuits, to reduce higher chip supply voltages to a level suitable for high performance circuit operation. State of the art switched-capacitor circuits inherently enable very high efficiency for ratioed conversion. For example, a 2:1 down conversion (0.5) has demonstrated at 90% efficiency. Such a voltage converter enables much higher supply voltage delivery to the chip for powering lower voltage circuit, e.g., providing a 2.0V supply to the chip may be converted down to 1.0V on-chip for 1V circuits. Linear regulators, which have been used for voltage conversion at ratios above 0.5, also achieve >90% efficiency for conversion at the higher performance end of the output voltage range, e.g., 1.3V to >1.2V conversion. However, efficiency falls off dramatically at the lower end of the output voltage range, e.g., ˜50% for 1.3V→0.7V conversion and below.
Thus, there is a need for a high efficiency voltage converter for on-chip voltage conversion that provides uniform efficiency across a wide conversion range; and more particularly, a variable conversion ratio on-chip voltage converter, and especially a variable voltage switched-capacitor converter, that exhibits a high efficiency even at the lower end of the voltage conversion range.